ATHENS — For eight decades, the iconic Hagia Sophia museum in Istanbul has stood as a symbol of Turkey's commitment to a secular society. Now that tradition is under siege by growing calls to convert the historic structure back into a practicing mosque.

The 1,500-year-old structure originally was built as an Orthodox Christian cathedral. It was turned into a mosque in the 15th century after the Ottoman Turks defeated the Greek emperor in Constantinople and renamed the city Istanbul. In the 1930s, the founder of modern Turkey, Kemal Ataturk, turned it into a museum in his drive to create a secular republic on the ruins of the Ottoman Empire.